Hi, I am developing an application which I want to be "100% fully compliant" across different Java EE vendors. Now it is a simple RESTful web application. The application works perfectly in Apache TomEE and Glassfish but not in Wildfly 8.1.0. Concretely it fails when try to unmarshal a rest call. Let me show an example (I have created one to make easy to follow).

I'm not sure the JAX-RS 2.0 Client API is required to automatically unmarshal JSON into an object. That exception to me looks like it's trying to unmarshal the body as JAXB (so in your case, it's looking for <bookInfo><title> ...). You can try changing request() to request(MediaType.APPLICATION_JSON_TYPE) to further indicate what you expect, but I think you're going to have to implement a JAX-RS MessageBodyReader that handles the JSON.